In various applications, it is desirable to use COG as both a reducing gas for producing DRI and as steel mill fuel gas. Conventionally, however, this presented problems due to the high level of hydrocarbons present in the COG, DRI sulfur issues, and the requirement for CO2 removal from the recycle gas.
Thus, in various exemplary embodiments, the present invention provides for the use of COG as both a both a reducing gas for producing DRI and as steel mill fuel gas. The COG is first compressed, then passed through an activated charcoal bed to remove the tars. Then, the COG is passed through a pressure swing absorption (PSA) unit or the like to create a high-purity H2 stream (about 99% purity) to be used as reducing gas in the direct reduction shaft furnace. The high purity H2 stream represents approximately 75% of the H2 in the COG and approximately 40% of the total COG stream. The remainder of the COG (including all of the sulfur and almost all of the hydrocarbons), about 60% of the COG total, is directed to a steel mill as fuel gas. As a result of using high purity H2 as reducing gas, the endothermic (heat consuming) hydrocarbon cracking and reforming reactions in the direct reduction shaft furnace are avoided, DRI sulfur issues are not present, and there is no requirement for CO2 removal from the recycle gas, with water advantageously being the primary by-product of the direct reduction reactions. Both once-through and recycle options are presented. Optionally, BOFG can be added to the reducing gas stream.